1. Field of the Invention
This invention relates generally to microprogrammed data processing systems and more particularly to the generation and storage of the leading zero count of the operand that is to be processed in accordance with a decimal numeric computer instruction.
2. Description of the Prior Art
Data processing systems process data stored in memory in the form of an operand consisting of decimal digits. The field in memory assigned to storing a particular operand contains as many memory locations for storing the operand as would be required to store the largest possible number of decimal digits for that operand.
In many cases the operand stored in that field in memory would require fewer decimal digits than does the maximum, therefore the memory field is filled in with zeros to the left of the most significant character of the operand, i.e., leading zero digits.
In the processing of computer instructions calling for a decimal arithmetic operation, the speed at which decimal arithmetic instructions are processed is increased if the system stores the number of leading zero digits in the operand.
The Honeywell 6000 large scale computing system had a relatively complicated scheme for counting the number of leading zero digits. In that system the high order data words containing a plurality of decimal digits were stored in a register on the first cycle. The word in the register was then examined on the second cycle, under control of special timing gates, for the number of leading zero digits contained in the data word. The special handling of the leading zeros required considerable logic thereby increasing the system cost and an additional cycle of delay thereby reducing the throughput during the processing of decimal numeric instructions.